The wheel driving system of excavator is developed towards high speed.Different system of chassis was differed in shift devices.The chassis driving and hydraulic system models of the wheel excavator based on AMESim were built by taking one type of hydraulic shifting system as an analysis object.Models of shift valves models were constructed by the basic components in HCD library.The shifting operation was researched by simulation.The effects of shift valve on velocity shift were analyzed.The defects of initial design of shift valve were found out.The valve body and spool were redesigned.Flow area was calculated through programming.The results of improved design show that different velocity shifts are made smoothly,which helps to reduce shift impact.